The German Patent No. 37 06 765 A1 discloses a crash (impact) sensor for a vehicle that comprises a test circuit. To be able to check the reliability of the crash sensor, an electro-acoustical transducer is provided, which acoustically exposes the acceleration sensor present in the crash sensor to ultrasonic waves. The electrical signals output by the acceleration sensor are checked in an evaluation and trigger circuit with respect to defined criteria with the help of a test circuit.
In addition, the German Patent No. 37 36 294 A1 discloses a device for testing acceleration sensors for correct functioning, where one or more accelerometers are electrically excited in such a way that one of the sensors acts as a transmitter of structure-borne noise, while the other(s) receives its signals. The accelerometers are thus checked by means of an evaluation circuit for functioning, calibration and coupling into the housing structure.
The German Patent No. 35 42 397 A1 discloses an arrangement for testing piezoelectric accelerometers for correct functioning, which uses a plurality of piezoelectric elements provided with electrodes, at least one of which, as a measuring sensor, produces an electrical reaction voltage when a force caused by the acceleration to be taken up is applied to it, and in the case of which, at least one of the piezoelectric elements acts for a time as an actuator for the other piezoelement, in that an electrical test voltage is supplied to the electrodes of the actuator element.
Furthermore, the U.S. Pat. No. 3,830,091 discloses a test device for acceleration sensors, which uses an aluminum rod, which is able to be excited to vibrate by piezoelectric crystals. A reference accelerometer and the accelerometer to be tested are mounted on the end face of the aluminum rod. An evaluation circuit compares the output signals from both of the accelerometers mounted on the end face of the aluminum rod, which are excited by the vibrating aluminum rod.
In addition, the U.S. Pat. No. 3,120,622 discloses a self-calibrating accelerometer, which uses an acceleration-sensitive element and, closely associated with said element, a piezoelectric element. When electrically excited, this piezoelectric element produces mechanical vibrations and, consequently, excites the acceleration-sensitive element.
Finally, the German Patent Application No. 38 09 299 C2 discloses an electronic device having an oscillatory sensor and an evaluation circuit for evaluating an output signal from the sensor that appears when said sensor is subjected to an acceleration load. This reference uses a vibration generator in the vicinity of the sensor capable of exciting the sensor to vibrate mechanically, the sensor being able to be excited for testing purposes by the vibration generator to produce vibrations which also include the resonant frequency of the sensor.